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Histological features cocker spaniel (8.8), shih tzu (4.6), Lhasa apso (4.5), Pekingese The tubules that make up the neoplasm are lined by a double layer (3.9), and toy poodle (3.4). No sex predilection has been noted. of epithelial cells and may contain an eosinophilic secretion. When compared with apocrine ductal adenomas the epithelial cells often Gross morphology are multilayered and there is nuclear and cellular pleomorphism, These neoplasms present as masses within the ear canal, including nuclear hyperchromasia, and moderate mitotic activity but seldom the vertical ear canal. Ulceration and secondary infection are the extensive pleomorphism seen with apocrine Foci of common. Benign neoplasms tend to be exophytic, especially in squamous differentiation are scattered throughout the neoplasm. dogs. It is often difficult to differentiate benign neoplasms from Peripheral invasion may be found but lymphatic invasion is infre- severe hyperplastic polypoid otitis externa, especially in the cocker quently observed (Figure 4.19H). spaniel. Some of the neoplasms are dark brown, probably secondary to retention of inspissated cerumen within the lumina Growth and metastasis of neoplastic In cats, these neoplasms must be differenti- These neoplasms are relatively slow growing, and most are ame- ated from inflammatory polyps of the external ear, which arise nable to surgical excision with wide margins. Metastases are very from the middle ear and extend through the tympanic membrane uncommon. into the external ear; these inflammatory polyps usually occur in younger cats. Complex and mixed apocrine carcinoma Complex apocrine carcinomas show proliferation of the glandular Histological features epithelium, which is malignant, and myoepithelial cells. In mixed Ceruminous adenomas are similar on histology to their cutaneous apocrine carcinomas the myoepithelial cells show chondroid or counterpart, the apocrine However, there is often reten- osseous metaplasia. tion of brown material within the glandular lumina, and small Complex and mixed apocrine carcinomas are rare in all species. brown globules within the cytoplasm of the neoplastic glandular In complex apocrine carcinomas the neoplastic apocrine cells show epithelium. Many neoplasms also show aggregation of pigment- pleomorphism and mitotic activity, and there is an accompanying laden macrophages within the interstitium, neutrophils within the periglandular proliferation of the myoepithelial cells. The mixed glandular lumina, and plasma cells in the periglandular stroma. apocrine carcinomas will show chondroid and occasionally osseous Occasional cases show invasion of neoplastic cells into the metaplasia of the myoepithelial cells. intraepidermal ductal portion of the gland (acrosyringium), with intraepidermal nests of neoplastic cells (Figure 4.20A). Ceruminous adenoma Superimposed inflammation often makes it difficult to differen- This is a benign tumor showing differentiation to ceruminous tiate benign from malignant ceruminous neoplasms, as the secretory epithelium. neoplastic cells appearing more pleomorphic and the nuclei more chromatic However, large, hyperchromatic nuclei with prominent Incidence, age, breed, and sex nucleoli and invasion through the basal lamina zone are not seen in Benign ceruminous neoplasms are relatively common in dogs Hyperplastic lesions of the external ear canal are more and cats between 4 and 13 years of age, with the peak incidence diffuse with marked epidermal hyperplasia, sebaceous gland between 7 and 10 years of age. Dog breeds at increased risk are and ceruminous gland hyperplasia, and severe chronic active A B Figure 4.20 (A) Ceruminous adenoma, canine. (B) Ceruminous carcinoma, 120 Tumors in Domestic Animals inflammation of the ceruminous glands and interstitial connective Complex and mixed ceruminous carcinoma tissue. Inflammatory polyps in the cat arise from the middle ear and The complex ceruminous carcinoma shows malignant proliferation often have ciliated cells or squamous epithelium on the surface, sub- of glandular epithelium and a proliferation of myoepithelial cells; epithelial aggregates of seromucinous glands, and an abundant mixed ceruminous carcinomas will have foci of chondroid or connective tissue stroma infiltrated by lymphocytes and plasma osseous metaplasia of the myoepithelium. cells often with germinal follicle formation. Incidence Growth Complex and mixed ceruminous carcinoma is very uncommon in The growth rate of these neoplasms is usually slow. However, the dog and rare or not reported in other species. complete surgical excision of the mass may be difficult to achieve, so that surgical ablation of the ear may be necessary. Histological features The histology of complex ceruminous carcinomas and mixed Complex and mixed ceruminous adenoma ceruminous carcinomas have features as described for their apo- Complex (compound) ceruminous neoplasms have glandular and crine counterparts. The designation of malignant is based on the myoepithelial cell and mixed ceruminous neoplasms show meta- general features of invasion and cellular and nuclear pleomorphism. plastic change of the myoepithelium to cartilage and bone. This is Too few cases have been seen to predict biologic behavior. similar to apocrine tumors that arise in the skin or mammary glands. Anal sac gland neoplasms General considerations Incidence, age, breed, and sex The anal sacs of the dog and cat are paired structures located on the Complex and mixed ceruminous adenomas are uncommon in the ventrolateral aspect of the anal area, between the external and dog and rare in other species. In dogs the peak incidence is between internal anal sphincter muscles. A short excretory duct is inter- 7 and 12 years of age. The breed at increased risk is the cocker posed between the anal sac and the glabrous skin of the anal area. spaniel (8.8). No sex predilection has been noted. The anal sac and duct are lined by a stratified squamous epithelium. Several large sebaceous glands empty into the neck region of the Gross morphology and histological features anal sac. Numerous apocrine glands, referred to as the apocrine These neoplasms cannot be differentiated from other ceruminous glands of the anal sac, open via ducts into the anal sac. neoplasms on gross inspection. Complex ceruminous neoplasms and mixed ceruminous neoplasms have histologic features identical Anal sac gland adenoma to those of their apocrine and mammary counterparts but the This is a benign neoplasm arising from the apocrine secretory tumor is in the ear canal. epithelium found in the wall of the anal sac. This tumor is very rare in both dogs and cats. Ceruminous gland carcinoma This is a malignant neoplasm showing differentiation to cerumi- Sites and gross morphology nous epithelium. Ceruminous carcinomas are more common in The neoplasm only arises in the area of the anal sac and cannot be cats than ceruminous adenomas, with the peak incidence between differentiated from its malignant counterpart, which is described 7 and 13 years of age. Domestic shorthaired cats (1.6) are predis- below. posed to developing the neoplasm. They are less common in dogs, occur between 5 and 12 years of age, with the peak incidence Histological features